The present invention relates to a method for checking the presence or absence of an X-ray sheet film in a cassette which had been inserted and opened in an apparatus for unloading or loading X-ray sheet films from or into the cassette, the cassette including a bottom part and a cover part hinged to a side of the bottom part, whereby an orderly loaded sheet film is deposited on a supporting foil provided with an electrically, magnetically or capacitively active element, and the apparatus including means for gripping the sheet film, such as for example a suction cup, and removing the film from the supporting foil. The invention also relates to a cassette charging and discharging apparatus operating in accordance with the method of this invention.
Apparatuses of the above-described kind for receiving and discharging X-ray film sheet cassettes are known from DE-OS No. 33 06 720 and DE-OS No. 37 12 964 wherein by means of an infrared light reflecting sensor the bottom of a cassette, opened after its insertion into the apparatus, is sensed. The disadvantage of the first-mentioned prior art device is its relatively low operational reliability because the difference between the reflection from the film and the amplifying foil which is utilized for determining the presence or the absence of a film, is too small. The second-mentioned device in order to eliminate this shortcoming provides a special reflector in a surface area of the amplifying foil in the path of propagation of the infrared light. This design, however, has the disadvantage that cassettes which are not provided with a reflector cannot be used.
Known are also X-ray sheet film cassettes wherein a steel foil or a magnetic foil is arranged in the bottom part of the cassette below the amplifying foil, the amplifying foil being glued to the steel foil at discrete points only and both foils being flexibly mounted in the bottom part of the cassette so as to be movable within certain limits. Cassettes of this kind have been described in DE-PS No. 32 30 287 and in practice are used in connection with a cassette unloading or loading apparatus according to DE-PS No. 32 32 187, for example. In this arrangement a sensor or scanning device is provided which detects whether a film is present in a cassette inserted into the unloading or loading apparatus, or not. The sensing or scanning is functionally reliable due to the fact that the cassettes are provided with an indicator knob which signals at the outside whether a sheet film is present in the cassette, that is it includes an additional feature according to the DE-PS No. 28 38 058. The indicator knob is particularly useful during an X-ray picture taking because the user can immediately recognize on the closed cassette whether it contains a film. The sensing or scanning of the indicator knob in the cassette unloading and loading apparatus is not only mechanically expensive, but has also the disadvantage that the sensing of the indicator knob on the outer surface of the cassette does not recognize whether during the opening of the cassette the film among other possibilities does not adhere to the cover of the cassette and consequently is not available in the bottom part for removal and thus a malfunction may result.